Sunflow is an advanced and highly extensible ray-tracing engine supporting
global illumination. It is written in Java (for extensibility) and the
source code is released under the MIT license. The current release is mainly
targeted to programmers. The scene file format is documented but no
exporters are provided as it is likely to change in the very near future.

Note: I am looking for talented modelers (3ds max preferably) to design some
additional test scenes and stress test the renderer. Feel free to contact me
if you are interested. Your work will be showcased and credited.